Personally calls like "Bigbird xxx maintain heading due crossing traffic 10 o'clock same level call clear of traffic" make me cringe. How can we assume that the traffic we think we've identified is the one he intended? We cannot. Thus taking the authority for avoidance based on our own unverifiable visual criteria is surely a nonsense in the controlled IFR environment? Dosen't this negate the entire point of IFR altogether?
My answer to the above is invariably "not visual", as per our flight plan.
Lookout in IMC/IFR? How?
Incoming!!!
Well, maybe it may be so that you are not the only dot on the ATCOs scope? Hence, by calling him he will be able to focus his attention you again. Confirming for himself that you are clear, and issue you your climb/descend, what-ever clearance.
But if you prefer not to help and give this information this is of course your prerogative. Of course you can always call him 5 mins later with "Bigbird xxx, we're still maintaining flxxx", when he forgotten all about your request for another level.
Besides from that IFR flightplan does not imply that you are IMC or VMC. As long as you are VMC, lookout is required. Procedures for lost com is also different depending IMC or VMC. Hence you can't say that your are IMC because you filed and IFR flightplan.
Last but not least, Class E airspace may contain uncontrolled VFR traffic. A good lookout + reduced speed may be very advisable.